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SubjectRe: puting task to TASK_INTERRUPTIBLE before adding it to an wait queue
On 3/17/06, Yitzchak Eidus <ieidus@gmail.com> wrote:
> the function worker_thread in kernel 2.6.15.6 first put the task to
> TASK_INTERRUPTIBLE and only then add itself to an wait queue:
> set_current_state(TASK_INTERRUPTIBLE);
> while (!kthread_should_stop()) {
> add_wait_queue(&cwq->more_work, &wait);
> ....
> my question is, what will happen if the timeslice for the
> worker_thread will finished just before it add itself to the wait
> queue?
> wont it call schedule() that will find the task is in
> TASK_INTERRUPTIBLE state and remove it from the runqueue? ( that what
> schedule() should do no? )
> and then how will the kernel be able to call to worker_thread ever if
> it isnt in any list???
> thanks for the comments!
>

more over the whole loop look like that:
set_current_state(TASK_INTERRUPTIBLE);
while (!kthread_should_stop()) {
add_wait_queue(&cwq->more_work, &wait);
if (list_empty(&cwq->worklist))
schedule();
else
__set_current_state(TASK_RUNNING);
remove_wait_queue(&cwq->more_work, &wait);

if (!list_empty(&cwq->worklist))
run_workqueue(cwq);
set_current_state(TASK_INTERRUPTIBLE);
}

what was the logic of putting the
set_current_state(TASK_INTERRUPTIBLE); before the loop and in the last
statement of the loop?

why not use something like this:
while (!kthread_should_stop()) {
add_wait_queue(&cwq->more_work, &wait);
set_current_state(TASK_INTERRUPTIBLE);
if (list_empty(&cwq->worklist))
schedule();
else
__set_current_state(TASK_RUNNING);
remove_wait_queue(&cwq->more_work, &wait);

if (!list_empty(&cwq->worklist))
run_workqueue(cwq);
}
that do the same thing without putting the task before the loop and in
the loop...?
( unless i am missing something? )
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